1. Field of the Invention
The invention relates to a suspended steam boiler including a steam boiler upper part, comprising a vertical tube wall, composed of vertical tubes and vertical web formed there between and a steam lower portion suspended from the vertical tube wall including an inclined tube wall composed of inclined tubes and inclined webs formed there between.
2. Description of the Related Art
The walls of larger sized steam boilers operating according to the forced once-through principle or forced circulation principle are nowadays designed as diaphragm tube walls composed of tube and web constructions. In order for the boilers to be able to expand freely, they are suspended in a boiler scaffolding. For that purpose, the boiler scaffolding includes a boiler scaffolding top, in which the supporting cables of the steam boiler are suspended. Accordingly, the entire weight of the steam boiler is absorbed by the boiler scaffolding top.
The steam boiler, in turn, must be so designed that the total weight comprising its own weight, the water content, ashes and the like, can be taken up by the boiler scaffolding top. The steam boiler upper portion includes membrane tube walls wherein the tubes are vertically disposed, and through which the medium flows in vertical direction (here denoted as vertical tube wall). On the other hand, in the steam boiler lower portion, the combustion chamber is surrounded by membrane tube walls which are not vertical but which rise at an incline to the horizontal (here denoted as inclined tube wall).
The load absorption takes place in the vertical tube wall of the steam boiler along the longitudinal axis of the vertical tubes, so that these are placed under tensile load in the direction of the tube axes.
On the other hand, in the lower portion of the steam boiler the load absorption takes place in the inclined tube wall at low angles of inclination transversely to the longitudinal axis of the inclined tubes. Accordingly, in this case, part of the loads arising is transferred to the tube cross section which, by comparison with the tube axis, is weaker.
In order to relieve these tube cross sections of loads it is, for example, known from DE 26 21 189 B to support the steam boiler lower portion on additional external tensile or load bearing elements which are anchored to the steam boiler upper portion. The tensile element extends more particularly in the form of tensile straps over the entire height of the inclined tube wall to which they are connected by way of filler members, welding-on blocks or clamping means, and terminate slightly above the inclined tube wall on the vertical tube wall to which they are welded by way of tensile strap heads, moulded members, welding-in panels, metal sheets, lugs or other connecting members. Accordingly, the load is transferred by the tensile or support elements from the steam boiler lower portion including the inclined tube wall into the vertical tube wall of the steam boiler upper portion.
With such external tensile elements which are welded by way of connecting members to the inclined tube wall, it is necessary, however, to ensure a good heat transfer from the tube walls to the tensile elements. In spite of this, load fluctuations occur, in particular in the inclined tube wall during each load change of the steam boiler resulting from a delayed following-up by the tensile element as against the membrane tube wall. Moreover, the application of the numerous connections of the tensile elements to the inclined tube wall involves an appreciable construction and welding expenditure. According to a further proposal known from DE 23 16 135 A the steam boiler lower portion which is directly welded to the vertical tubing of the steam boiler upper portion is, therefore, supported while its tube plate by way of linkage supports on support elements in the form of beams which are in their turn suspended by way of tensile anchors from the vertical tube wall of the steam boiler upper portion. However, this known proposal itself involves a substantial constructional expenditure combined with an increased weight due to the support element which must be absorbed by the vertical tube wall.